Carla Bruni-Sarkozy, the wife of the French president, obtained police and intelligence service reports to discover who was spreading rumours that she and her husband were having affairs, a new authorised biography claims.

The authors of Carla and the Ambitious say Bruni-Sarkozy used confidential records of telephone calls and text messages to confront plotters who were allegedly trying to oust her, including the former justice minister Rachida Dati.

The allegation comes as President Nicolas Sarkozy faces an embarrassing investigation into reports that the Elysée Palace ordered France's counter-espionage services to spy on Le Monde journalists to identify the source of leaks in the political scandal surrounding the L'Oréal heiress Liliane Bettencourt.

Unsubstantiated and vehemently denied rumours that both he and his wife were having affairs emerged in March.

It was suggested at the time that the couple had called on the security services to find out who was behind the rumours, but no firm evidence of this emerged. Now, journalists Michaël Darmon and Yves Derai say the Elysée received a full police report suggesting there had been a plot by Dati, a former favourite of the president who was later sacked from the cabinet, and a second woman once married to Sarkozy's younger brother.

The authors say agents identified the plotters through phone calls and text messages and suggested the culprits tried to involve others, including the head of a lobby group. Believing Bruni-Sarkozy to be the president's "weak link" and an easy target, the plotters allegedly aimed to persuade Sarkozy's former wife, Cécilia Attias, from whom he had split a few months after he was elected in 2007, to return to his side.

Le Parisien newspaper said that as soon as she had the report in her hands, Bruni-Sarkozy called her predecessor, who now lives in New York, informing her: "Two people with whom you are in contact are behaving in an unacceptable manner towards us … I am not talking about suspicious or malicious gossip. I have a police report that you are welcome to see. I know you have nothing to do with them but I suggest you keep your distance."

Darmon and Derai say police examined the phone records of several well-known "personalities" suspected of being involved in spreading the rumours.

In April Dati (below) issued a statement in which she "protested with indignation against allegations in certain press organs that she was responsible in any way for the propagation of absurd and inadmissible rumours about the private life of the presidential couple."

But quickly Sarkozy took his revenge. Here official car and bodyguards were withdrawn while she was doing a television interview on the evening of the regional elections.

TheyDarmon and Derai said Dati, distressed at being dumped from the government, would "stop at nothing to return to such dizzying heights". She and a second alleged plotter, Sophie Douzal, the former wife of the president's brother François Sarkozy, are nicknamed the "Stiletto Heel Firm" in the book.

Once she had the evidence implicating the two women Bruni-Sarkozy apparently rang Douzal, who calls herself Sophie Sarkozy, to berate her and tell her that she no longer had the right to use the president's family name.

The book, which came out today is the second biography of Bruni-Sarkozy to appear in a week. Carla – A Secret Life was an unflattering portrayal of her as a Marie-Antoinette figure more concerned with ex-boyfriends and cosmetic surgery than representing France on the world stage.

Darmon, an Elysée accredited journalist for the broadcaster France 2, and Derai are close to the presidential couple. The journalists' book was written with Bruni-Sarkozy's co-operation and approval.

The claim that the presidential couple made use of the secret services also comes at time when Sarkozy is facing domestic and international censure over France's deportation of nearly 1,000 Romas and a second case of unauthorised use of spies.

This week, Le Monde launched a lawsuit for breach of confidentiality of sources, accusing the Elysée of using illegally using the domestic intelligence agency, the DCRI – the equivalent of MI5 – to trace the source of leaks from police interviews with witnesses in the Bettencourt party-funding scandal.

The source, a top official in the justice ministry, has since been removed from his post and packed off to the French overseas department of French Guiana in South America, home to Devil's Island, the former prison colony which housed Alfred Dreyfus.

French intelligence and police services insisted the investigation into the Sarkozy marriage rumours was carried out on the orders of Elysée advisors who feared an attempt to "destabilise" the president and not the couple themselves.

Dati has always denied being behind the rumours and has apparently consulted lawyers about the book. She has made no comment and neither has the Elysée.